1. Field of the Invention
This invention relates to a driving device, and more particularly to a motor stator.
2. Description of the Related Art
Referring to FIG. 1, a conventional heat-dissipating fan 1 includes an outer housing 11, a stator 12 disposed on the outer housing 11, and a rotor 13 disposed pivotally on the outer housing 11.
The outer housing 11 includes a tubular shaft 111. The stator 12 includes a stator frame 121 sleeved on the shaft 111, a plurality of superposed silicone steel sheets 122 fixed on the stator frame 121, and a plurality of induction coils 123 wound around the stator frame 121.
The rotor 13 includes a hub 131 disposed rotatably on the shaft 111 for covering the stator 12, a plurality of blades 132 extending outwardly from an outer peripheral surface of the hub 131, and a ring-shaped magnet 133 disposed fixedly on an inner peripheral surface of the hub 131 and spaced apart from and disposed around the stator 12.
When the induction coils 123 are energized, a repulsive magnetic force is created between the ring-shaped magnet 133 and the silicone steel sheets 122 to drive rotation of the ring-shaped magnet 133 and, thus, the rotor 13 relative to the stator 12.
Since both the silicone steel sheets 122 and the induction coils 123 are disposed on the stator frame 121, the stator 12 of the heat-dissipating fan 1 is relatively high (i.e., thick), thereby limiting the applicable range of the fan 1.
A thin motor stator has been proposed to solve the applicable range problem of the aforesaid conventional heat-dissipating fan 1. For example, referring to FIG. 2, in a thin fan disclosed in Taiwanese Patent Publication No. 1332058, a bearing 21, a hub 22, an iron-contained metallic sheet 23, and a magnet 24 are integrated to constitute a rotating member 20. The rotating member 20 is driven by a coil circuit board 25 embedded with a plurality of coil windings 251. As such, the height of the fan is reduced to increase the applicable range of the fan.
As well known in the art that, the more the turn numbers of the coil windings 251, the more the intensity of the magnetic field generated after the coil windings 251 are energized. However, since the area of the coil circuit board 25 is relative small, the turn numbers of the coil windings 251 are limited so that, when the coil windings 251 are energized, the magnetic field intensity thus generated is small. As a consequence, the rotational speed of the hub 22 is also small, thereby resulting in difficulties when driving rotation of the hub 22.